BLT/include/blt/fs/filesystem.h

/*
 *  <Short Description>
 *  Copyright (C) 2024  Brett Terpstra
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#ifndef BLT_FILESYSTEM_H
#define BLT_FILESYSTEM_H

#include <fstream>
#include <ios>

namespace blt::fs
{
    /**
     * A simple interface which provides a way of reading the next block of data from a resource.
     * The interface provides a single function "read" which will read a specified number of bytes into the buffer.
     * The implementation for this could be fstreams, zlib deflate, or any method filesystem access.
     * Reading of a large number of bytes ( > block size) is guaranteed to not significantly increase the read time and will likely result in a
     * direct passthrough to the underlying system. Small reads will be buffered, hence the name "block" reader.
     */
    class block_reader
    {
        protected:
            // 32768 block size seems the fastest on my system
            unsigned long m_bufferSize;
        public:
            explicit block_reader(size_t bufferSize): m_bufferSize(bufferSize)
            {}
            
            /**
             * Reads bytes from the internal filesystem implementation
             * @param buffer buffer to copy the read bytes into
             * @param bytes number of bytes to read
             * @return status code. non-zero return codes indicates a failure has occurred.
             */
            virtual int read(char* buffer, size_t bytes) = 0;
            
            virtual size_t gcount() = 0;
            
            virtual char get()
            {
                char c[1];
                read(c, 1);
                return c[0];
            }
    };
    
    /**
     * A buffered block writer without a definite backend implementation. Exactly the same as a block_reader but for writing to the filesystem.
     */
    class block_writer
    {
        protected:
            unsigned long m_bufferSize;
        public:
            explicit block_writer(unsigned long bufferSize): m_bufferSize(bufferSize)
            {}
            
            /**
             * Writes the bytes to the filesystem backend implementation
             * @param buffer bytes to write
             * @param bytes number of bytes to write
             * @return non-zero code if failure
             */
            virtual int write(char* buffer, size_t bytes) = 0;
            
            virtual int put(char c)
            {
                char a[1];
                a[0] = c;
                return write(a, 1);
            }
            
            /**
             * Ensures that the internal buffer is written to the filesystem.
             */
            virtual void flush() = 0;
    };
    
    /**
     * fstream implementation of the block reader.
     */
    class fstream_block_reader : public block_reader
    {
        private:
            std::fstream& m_stream;
            char* m_buffer = nullptr;
            size_t readIndex = 0;
        public:
            explicit fstream_block_reader(std::fstream& stream, size_t bufferSize = 131072);
            
            explicit fstream_block_reader(fstream_block_reader& copy) = delete;
            
            explicit fstream_block_reader(fstream_block_reader&& move) = delete;
            
            fstream_block_reader& operator=(const fstream_block_reader& copy) = delete;
            
            fstream_block_reader& operator=(const fstream_block_reader&& move) = delete;
            
            int read(char* buffer, size_t bytes) override;
            
            size_t gcount() final
            {
                return m_stream.gcount();
            }
            
            ~fstream_block_reader()
            {
                delete[] m_buffer;
            }
    };
    
    class fstream_block_writer : public block_writer
    {
        private:
            std::fstream& m_stream;
            char* m_buffer;
            size_t writeIndex = 0;
            
            void flush_internal();
        
        public:
            explicit fstream_block_writer(std::fstream& stream, size_t bufferSize = 131072):
                    block_writer(bufferSize), m_stream(stream), m_buffer(new char[bufferSize])
            {}
            
            explicit fstream_block_writer(fstream_block_writer& copy) = delete;
            
            explicit fstream_block_writer(fstream_block_writer&& move) = delete;
            
            fstream_block_writer& operator=(const fstream_block_writer& copy) = delete;
            
            fstream_block_writer& operator=(const fstream_block_writer&& move) = delete;
            
            int write(char* buffer, size_t bytes) override;
            
            inline void flush() override
            {
                flush_internal();
            }
            
            ~fstream_block_writer()
            {
                flush_internal();
                delete[] m_buffer;
            }
    };
}

#endif //BLT_FILESYSTEM_H